The present invention relates to an optical pick-up apparatus, optical elements, and an objective lens, and specifically to an optical pick-up apparatus which can information-record on two optical information recording media whose transparent substrate thickness are different, or can information-reproduce from two optical information recording media whose transparent substrate (base plate) thickness are different, and to optical elements and an objective lens for use in the apparatus.
Recently, as a short wavelength red semiconductor laser is put to practical use, the development of a DVD (digital video disk) which is a high density optical disk whose size is almost the same as the conventional optical disk, that is, a CD (compact disk) which is an optical information medium, and whose capacity is greatly increased, is advanced. In an optical system of an optical information recording and reproducing apparatus which uses such the optical disk as a medium, in order to attain the high increase of the density of a recording signal, it is required that the diameter of a spot which is converged by an objective lens, is reduced. Therefore, there is a real situation in which the shortening of the wavelength of a laser as a light source and an increase of NA of the objective lens are promoted.
For example, in the optical pick-up apparatus for recording and/or reproducing the information on and from the DVD, when the short wavelength semiconductor laser of 635 nm is used as the light source, the numerical aperture NA of the objective lens to converge the laser light, on the optical disk side, is about 0.6. Incidentally, in the CD, or DVD, there are many kinds of standards of optical disks such as, for example, CD-R (Compact Disk-Recordable), and other than CD, or DVD, MD (Mini Disk)or the like, is put into the market, and comes into wide use.
On the one hand, in the optical pick-up apparatus to record the information and/or to reproduce the information on or from the CD-R, the light source having the wavelength xcex=780 nm is necessary, however, for the other optical disks, the light source having the wavelength other than the specific light source wavelength can be used, and in such the case, corresponding to the light source wavelength to be used, the necessary numerical aperture NA is changed. For example, the following values are approximated: in the case of CD, necessary numerical aperture NA=xcex (xcexcm)/1.73, and in the case of DVD, the necessary numerical aperture NA=xcex (xcexcm)/1.06. The numerical aperture in the present specification is the numerical aperture of a converging optical system viewed from the optical disk side, and the necessary numerical aperture is the numerical aperture calculated from a spot size d required on the recording surface of the optical disk and the wavelength to be used xcex, and generally, NA=0.83xc3x97xcex÷d.
As described above, various optical disks whose transparent substrate thickness, recording density, and wavelength to be used, are different from each other, exist in the market, and to purchase the exclusively used information recording and reproducing apparatus by which the information can be recorded and/or reproduced on or from each of optical disks, is a large burden on the user. Accordingly, an information recording and reproducing apparatus provided with the optical pick-up apparatus which can cope with various optical disks and is interchangeable, is proposed.
In such the optical pick-up apparatus, when the light flux having the different wavelength is entered into the substrates with the different thickness, it is necessary that the spherical aberration is corrected to a smaller amount than a predetermined amount, and in order to appropriately write and read the information, the spot diameter of each light flux is made to be within a predetermined range.
Accordingly, the optical pick-up apparatus which reproduces a plurality of optical disks by using one converging optical system is proposed. For example, in Japanese Tokkaihei No. 7-302437, the optical pick-up apparatus in which the refraction surface of the objective lens is divided into ring-like plural areas, and the information is reproduced when the light beam is image-formed on one of the optical disks with the different thickness, by each of the divided surfaces of the objective lens, is disclosed.
However, in the optical pick-up apparatus disclosed in Japanese Tokkaihei No. 7-302437, because one objective lens has more than 2 focal points simultaneously, and the spot light amount of the focal point per one is reduced, there is a problem that it is necessary to increase the laser output.
On the one hand, in Japanese Tokkaihei No. 10-142494, a 2 composition high NA lens for the pick-up, which can cope with 2 kinds of information recording media with different transparent substrate thickness, is shown. However, in the technique disclosed in this application, because, by changing the interval between 2 lenses, the lens copes with the transparent substrates with different thickness, there is a problem that the structure becomes complicated.
Further, in Japanese Tokkaihei No. 9-54973, an optical system using a hologram optical element by using the transmitted light (0-order diffracted ray) of 635 nm, and xe2x88x921 order diffracted ray of 785 nm, and an optical system using the hologram optical element by using +1 order diffracted ray of 635 nm, and the transmitted light (0-order diffracted ray) of 785 nm, are disclosed. However, according to this hologram optical element, because the difference in level of the hologram is large, the integration with the objective lens is difficult.
Further, in Japanese Tokkaihei No. 11-96585, the optical pick-up apparatus in which 3 divided surfaces are provided on the refraction surface on the light source side of the objective lens, and in the case of the reproduction of the first optical disk, the light flux passing through the first divided surface and the third divided surface is used, and in the case of the reproduction of the second optical disk whose transparent substrate thickness is different from the first optical disk, the light flux passing through the first divided surface and the second divided surface is used, is disclosed. However, according to this objective lens, the residual aberration becomes large on the optical disk (for example, CD) whose transparent substrate is thicker than the other.
Further, the present inventors previously proposed the optical pick-up apparatus in Japanese Tokuganhei No. 11-312701, in which the action of the diffraction surface and the refraction surface is cancelled for a plurality of light sources with different wavelengths and the spherical aberration is corrected by an objective lens on whose refractive surface the diffracting ring-shaped band is provided. In this case, there is a case where the chromatic aberration is generated, when the wavelength is changed in the light source whose wavelength is shorter than the other.
Incidentally, normally, in the optical pick-up apparatus, a detector to detect a tracking error or the like, when it receives the reflected light from the optical information recording medium, is provided. In the. conventional optical pick-up apparatus, because only the spot light is reflected from the optical information medium, as far as the spot light is irradiated on the correct recording position on the optical information recording medium, the possibility that the light is erroneously detected by the detector, is low. However, when the reflected light passes through the above objective lens, because the light flux more than a predetermined numerical aperture is irradiated on the optical information recording medium as a flare light, when the reflected light is detected by the detector, the possibility of the erroneous detection is generated.
In contrast to this, an optical pick-up apparatus in which respective converging optical systems corresponding to each of different optical disks are provided, and the converging optical systems are switched corresponding to the optical disk to be reproduced, is proposed. According to such the optical pick-up apparatus, when the light flux having different wavelengths are entered into the substrates having the different thickness, the spherical aberration can be corrected to not larger than a predetermined amount, and the spot diameter of each light flux can be within a predetermined range. However, in this optical pick-up apparatus, because a plurality of converging optical systems are necessary, the structure is complicated, and the cost becomes high, therefore, it is not preferable.
An object of the present invention is to provide an optical pick-up apparatus in which, although a small number of optical elements or objective lenses are used, the information can be recorded and/or reproduced (hereinafter, simply called recording and reproducing) for the information recording medium with the different thickness, and an objective lens and optical elements for use in that.
Further, another object of the present invention is, in the optical pick-up apparatus in which the information can be recorded and/or reproduced for the information recording medium with the different thickness, to provide an optical pick-up apparatus in which, even when the information recording medium whose necessary numerical aperture is not larger than the others is recorded and/or reproduced, the irradiation of unnecessary light to the optical detector can be prevented, and the detection accuracy can be increased.
An object of the present invention is to provide an objective lens, in which at least 2 kinds of optical information recording media having transparent substrates with different thickness can be reproduced or recorded by the light source with at least 2 wavelengths different from each other, and the chromatic aberration of the information recording medium with thinner transparent substrate can be reduced, and simultaneously, the residual aberration of the optical information recording medium with thicker transparent substrate can be reduced to a half, and an optical pick-up apparatus having a converging optical system including the objective lens.
An object of the present invention is to provide an objective lens which, in a high NA objective lens of 2 element-composition, can cope with the information recording media having the different thickness without changing the lens interval, and to provide an optical pick-up apparatus mounted with the objective lens.
An object of the present invention is to provide an optical element appropriate for an optical pick-up apparatus, which can record and/or reproduce the information (hereinafter, simply called recording and reproducing) for the optical information media with different thickness, although a few number of optical elements or objective lenses are used, and can suppresses the erroneous detection, and to provide an optical pick-up apparatus using the optical element.
Above objects can be attained by the following structures.
(1-1) An optical pickup apparatus to conduct reproducing and/or recording information of a first optical information recording medium including a first transparent base plate having a thickness of t1 and a second optical information recording medium including a second transparent base plate having a thickness of t2 (t2 greater than t1), comprises:
a first light source to emit a first light flux having a wavelength of xcex1;
a second light source to emit a second light flux having a wavelength of xcex2 (xcex1 less than xcex2)
a converging optical system to converge the first light flux or the second light flux onto a first information recording surface of the first optical information recording medium or a second information recording surface of the second optical information recording medium, the converging optical system having an objective lens; and
an optical detector to receive reflected light from the first optical information recording medium or the second optical information recording medium;
wherein the converging optical system comprises a diffracting section on an entire surface in an effective aperture or an almost entire surface in the effective aperture of at least one surface thereof,
the converging optical system generates a m-th order diffracted light ray (m being an integer other than zero) more than other order diffracted light rays when the first light flux passes the diffracting section and converges the m-th order diffracted light ray onto the first information recording surface so as to conduct the reproducing and/or recording information of the first optical information recording medium;
the converging optical system generates a n-th order diffracted light ray (n being an integer other than zero) more than other order diffracted light rays when the second light flux passes the diffracting section and converges the n-th order diffracted light ray onto the second information recording surface so as to conduct the reproducing and/or recording information of the second optical information recording medium; and
a spherical aberration has at least one discontinuous portion or at least one substantially discontinuous portion when the converging optical system converges the second light flux onto the second information recording surface so as to conduct reproducing and/or recording the information of the second optical information recording medium.
(1-2) In the optical pickup apparatus of (1-1), the following formula is satisfied:
m=n
(1-3) In the optical pickup apparatus of (1-1), when an optical path difference function of the diffracting surface is xcfx86(h) where h is a distance from the optical axis along the direction perpendicular to the optical axis at the surface provided with the diffracting section, dxcfx86(h)/dh is discontinuous or substantially discontinuous at at least one point, whereby a spherical aberration has at least one discontinuous portion or at least one substantially discontinuous portion when the converging optical system converges the second light flux onto the second information recording surface in order to conduct reproducing and/or recording the information of the second optical information recording medium.
(1-4) In the optical pickup apparatus of (1-3), the diffracting section has plural diffracting ring-shaped bands in which a prescribed ring-shaped band is located at the outermost side among inner ring-shaped bands located on an inside of the point of h where dxcfx86(h)/dh is discontinuous or substantially discontinuous and a neighbor ring-shaped band neighbors the prescribed ring-shaped band and is located on an outside of the point of h and, and wherein a width of the prescribed ring-shaped band along a direction perpendicular to an optical axis of the surface having the diffracting section is smaller than that of the neighbor ring-shaped band.
(1-5) In the optical pickup apparatus of (1-1), a necessary numerical aperture at an optical information recording medium-side of the converging optical system necessary to conduct recording or reproducing the information of the first optical information recording medium with the first light flux is NA1 and a necessary numerical aperture at an optical information recording medium-side of the converging optical system necessary to conduct recording or reproducing the information of the second optical information recording medium with the second light flux is NA2 (NA1 greater than NA2), and wherein among the second light flux having passed the objective lens, a light flux having passed a portion whose numerical aperture at the optical information recording media-side is not smaller than NA2 and is not larger than NA1 forms a spot on the second information recording surface through the second transparent base plate of the second optical information recording medium, a diameter of the spot is not smaller than w2 and is not larger than w1, and the following conditional formulas are satisfied:
10 xcexcmxe2x89xa6w2 xe2x89xa650 xcexcm
20 xcexcmxe2x89xa6w1xe2x88x92w2xe2x89xa6110 xcexcm
(1-6) In the optical pickup apparatus of (1-1), when the diffracting section is provided on an aspheric surface of the objective lens and a length x along an optical axis of the objective lens is x coordinate and a height h perpendicular to the optical axis is h coordinate, dx/dh is discontinuous or substantially discontinuous at at least one point on a basic aspheric surface of the aspheric surface provided with the diffracting section, whereby a spherical aberration has at least one discontinuous portion or at least one substantially discontinuous portion when the converging optical system converges the second light flux onto the second information recording surface in order to conduct reproducing and/or recording the information of the second optical information recording medium.
(1-7) In the optical pickup apparatus of (1-1), the diffracting section is provided on a surface of the objective lens and the objective lens has a stepped portion in an effective aperture.
(1-8) In the optical pickup apparatus of (1-1), a necessary numerical aperture at an optical information recording medium-side of the converging optical system necessary to conduct recording or reproducing the information of the first optical information recording medium with the first light flux is NA1 and a necessary numerical aperture at an optical information recording medium-side of the converging optical system necessary to conduct recording or reproducing the information of the second optical information recording medium with the second light flux is NA2 (NA1 greater than NA2), and wherein among the first light flux having passed the objective lens, when a first light flux having passed a portion of the objective lens whose numerical aperture at the optical information recording media-side is not larger than NA1 passes through the first transparent base plate of the first optical information recording medium, a wave front aberration of the first light flux on the first information recording surface is not larger than 0.07 xcex1 rms, and among the second light flux having passed the objective lens, when a second light flux having passed a portion of the objective lens whose numerical aperture at the optical information recording media-side is not larger than NA2 passes through the second transparent base plate of the second optical information recording medium, a wave front aberration of the second light flux on the second information recording surface is not larger than 0.07 xcex2 rms.
(1-9) In the optical pickup apparatus of (1-8), among the second light flux having passed the objective lens, when the second light flux having passed a portion the objective lens whose numerical aperture at the optical information recording media-side is not larger than NA2 passes through the second transparent base plate of the second optical information recording medium, a third-order spherical aberration component of the wave front aberration of the second light flux on the second information recording surface shows an over characteristic and an absolute value (WSA2xc2x7xcex2 rms) of the third-order spherical aberration component satisfies the following conditional formula:
0.02 xcex2 rmsxe2x89xa6WSA2xc2x7xcex2 rmsxe2x89xa60.06 xcex2 rms
(1-10) In the optical pickup apparatus of (1-8), among the first light flux having passed the objective lens, when the partial first light flux having passed a portion the objective lens whose numerical aperture at the optical information recording media-side is not larger than NA1 passes through the first transparent base plate of the first optical information recording medium, an absolute value (WSA1xc2x7xcex1 rms) of a third-order spherical aberration component of the wave front aberration of the partial first light flux on the first information recording surface satisfies the following conditional formula:
WSA1xc2x7xcex1 rmsxe2x89xa60.04 xcex1 rms
(1-11) In the optical pickup apparatus of (1-1), the spherical aberration has two or more discontinuous portions or two or more substantially discontinuous portions when the converging optical system converges the second light flux onto the second information recording surface in order to conduct reproducing and/or recording the information of the second optical information recording medium.
(1-12) In the optical pickup apparatus of (1-1), the objective lens is a single lens having a positive refracting power.
(1-13) In the optical pickup apparatus of (1-1), the objective lens comprises a first lens having a positive refracting power and a second lens having a positive refracting power.
(1-14) In the optical pickup apparatus of (1-1), the diffracting section comprises plural diffracting ring-shaped bands among which at least one diffracting ring-shaped band satisfies the following conditional formula:
1.2xe2x89xa6Pi+1/Pixe2x89xa610
where Pi is a width of the diffracting ring-shaped band located at i-th place counted from an optical axis of the surface provided with the diffracting section to a periphery of the lens in which the width is along the direction vertical to the optical axis.
(1-15) In the optical pickup apparatus of (1-1), a number m of a ring-shaped band through which a light ray of NA of 0.60 passes satisfies the following conditional formula:
22xe2x89xa6mxe2x89xa632
wherein a number of ring-shaped band located on an optical axis on a surface provided with the diffracting section is 1 and the number m is counted toward the periphery side.
(1-16) In the optical pickup apparatus of (1-1), a necessary numerical aperture at an optical information recording medium-side of the converging optical system necessary to conduct recording or reproducing the information of the first optical information recording medium with the first light flux is NA1 and a necessary numerical aperture at an optical information recording medium-side of the converging optical system necessary to conduct recording or reproducing the information of the second optical information recording medium with the second light flux is NA2 (NA1 greater than NA2), and wherein among the first light flux having passed the objective lens, when a first light flux having passed a portion of the objective lens whose numerical aperture at the optical information recording media-side is not larger than NA1 passes through the second transparent base plate of the second optical information recording medium, a wave front aberration of the first light flux on the first information recording surface is not larger than 0.07 xcex1 rms, and among the second light flux having passed the objective lens, when a partial second light flux having passed a portion of the objective lens whose numerical aperture at the optical information recording media-side is not larger than NA2 passes through the second transparent base plate of the second optical information recording medium, a wave front aberration of the partial second light flux on the second information recording surface is not larger than 0.07 xcex2 rms, and when another partial second light flux having passed a portion of the objective lens whose numerical aperture at the optical information recording media-side is larger than NA2 passes through the second transparent base plate of the second optical information recording medium, a wave front aberration of the another partial second light flux on the second information recording surface is larger than 0.07 xcex2 rms.
(1-17) In the optical pickup apparatus of (1-1), a numerical aperture of NAZ is a predetermined value which satisfies the following conditional formula:
0.43xe2x89xa6NAZxe2x89xa60.53, and
wherein among the second light flux having passed the objective lens, when a partial second light flux having passed a portion of the objective lens whose numerical aperture at the optical information recording media-side is not smaller than NAZ and not larger than 0.7 passes through the second transparent base plate of the second optical information recording medium and when another partial second light flux having passed a portion of the objective lens whose numerical aperture at the optical information recording media-side is smaller than NAZ passes through the second transparent base plate of the second optical information recording medium, an amount of spherical aberration of the partial second light flux is larger by 10 xcex2 or more than that of the another partial second light flux.
(1-18) In the optical pickup apparatus of (1-1), the optical detector comprises a light receiving surface arranged at a predetermined position and a numerical aperture of NAZ is a predetermined value which satisfies the following conditional formula:
0.43xe2x89xa6NAZxe2x89xa60.53, and
wherein among the second light flux having passed the objective lens, when a partial second light flux having passed a portion of the objective lens whose numerical aperture at the optical information recording media-side is smaller than NAZ passes through the second transparent base plate of the second optical information recording medium, reflected light of the partial second light flux from the second recording surface proceeds into the light receiving surface of the optical detector and when another partial second light flux having passed a portion of the objective lens whose numerical aperture at the optical information recording media-side is not smaller than NAZ passes through the second transparent base plate of the second optical information recording medium, reflected light of the another partial second light flux from the second recording surface proceeds into a periphery region other than the light receiving surface of the optical detector.
(1-19) In the optical pickup apparatus of (1-1), the optical detector comprises a central light receiving surface and a peripheral light receiving surface arranged at predetermined positions respectively and a numerical aperture of NAZ is a predetermined value which satisfies the following conditional formula:
0.43xe2x89xa6NAZxe2x89xa60.53, and
wherein among the second light flux having passed the objective lens, when a partial second light flux having passed a portion of the objective lens whose numerical aperture at the optical information recording media-side is not smaller than NAZ passes through the second transparent base plate of the second optical information recording medium, reflected light of the another partial second light flux from the second recording surface proceeds into the peripheral light receiving surface of the optical detector other than the central light receiving surface or a periphery region other than the periphery light receiving surface.
(1-20) In the optical pickup apparatus of (1-1), the diffracting section comprises a first diffracting section and a second diffracting section and an order number of a strongest diffracted light ray generated by the first diffracting section for a light flux having a predetermined wavelength and an order number of a strongest diffracted light ray generated by the second diffracting section for the light flux having the predetermined wavelength are different from each other and not zero respectively.
(1-21) In the optical pickup apparatus of (1-1), the diffracting section comprises a first diffracting section and a second diffracting section and an order number of a strongest diffracted light ray generated by the first diffracting section for a light flux having a predetermined wavelength and an order number of a strongest diffracted light ray generated by the second diffracting section for the light flux having the predetermined wavelength are same to each other and not zero respectively.
(1-22) An objective lens for use in an optical pickup apparatus to conduct reproducing and/or recording information of an optical information recording medium having a transparent base plate, comprises:
at least one surface;
wherein a diffracting section is provided on an entire surface of an effective aperture of the surface or an almost entire surface of the effective aperture of the surface, wherein when a light flux having a predetermined wavelength. passes the diffracting section, the objective lens generate a m-th order diffracted light ray (m being an integer other than zero) more than other order light rays and when the m-th order diffracted light ray is converged through a transparent base plate having a predetermined thickness, a spherical aberration has at least one discontinuous portion or at least one substantially discontinuous portion.
(1-23) In the objective lens of (1-21), the optical pickup apparatus conducts reproducing and/or recording information of a first optical information recording medium including a first transparent base plate having a thickness of t1 and a second optical information recording medium including a second transparent base plate having a thickness of t2 (t2 greater than t1),
when a first light flux having a wavelength of xcex1 passes the diffracting section, the objective lens generates the m-th order diffracted light ray (m being an integer other than zero) more than other order diffracted light rays and converges the m-th order diffracted light rays onto a first information recording surface so that the optical pickup apparatus conducts the reproducing and/or recording information of the first optical information recording medium;
when a second light flux having a wavelength of xcex2 (xcex1 less than xcex2) passes the diffracting section, the objective lens generates the n-th order diffracted light ray (n being an integer other than zero) more than other order diffracted light rays and converges the n-th order diffracted light rays onto a second information recording surface so that the optical pickup apparatus conducts the reproducing and/or recording information of the second optical information recording medium; and
when the objective lens converges the second light flux onto the second information recording surface, a spherical aberration has at least one discontinuous portion or at least one substantially discontinuous portion.
(1-24) In the objective lens of (1-23), the following formula is satisfied:
m=n
(1-25) In the objective lens of (1-23), when an optical path difference function of the diffracting surface is xcfx86(h) where h is a distance from the optical axis, dxcfx86(h)/dh is discontinuous or substantially discontinuous at at least one point, whereby a spherical aberration has at least one discontinuous portion or at least one substantially discontinuous portion when the converging optical system converges the second light flux onto the second information recording surface in order to conduct reproducing and/or recording the information of the second optical information recording medium.
(1-26) In the objective lens of (1-25), the diffracting section has plural diffracting ring-shaped bands in which a prescribed ring-shaped band is located at the outermost side among inner ring-shaped bands located on an inside of the point of h where dxcfx86(h)/dh is discontinuous or substantially discontinuous and a neighbor ring-shaped band neighbors the prescribed ring-shaped band and is located on an outside of the point of h and, and wherein a width of the prescribed ring-shaped band along a direction perpendicular to an optical axis of the surface having the diffracting section is smaller than that of the neighbor ring-shaped band.
(1-27) In the objective lens of (1-23), when the objective lens has an aspheric surface and a length x along an optical axis of the objective lens is x coordinate and a height h perpendicular to the optical axis is h coordinate, dx/dh is discontinuous or substantially discontinuous at at least one point on a basic aspheric surface of the aspheric surface.
(1-28) In the objective lens of (1-23), the objective lens has a stepped portion in an effective aperture.
(1-29) In the objective lens of (1-23), when the objective lens converges the second light flux onto the second information recording surface in order to conduct reproducing and/or recording the information of the second optical information recording medium, a spherical aberration has at least two discontinuous portion or at least two substantially discontinuous portion.
(1-30) In the objective lens of (1-22), the objective lens is a single lens having a positive refracting power.
(1-31) In the objective lens of (1-22), the objective lens comprises a first lens having a positive refracting power and a second lens having a positive refracting power.
(1-32) In the objective lens of (1-22), the diffracting section comprises plural diffracting ring-shaped bands among which at least one diffracting ring-shaped band satisfies the following conditional formula:
1.2xe2x89xa6Pi+1/Pixe2x89xa610
where Pi is a width of the diffracting ring-shaped band located at i-th place counted from an optical axis of the surface provided with the diffracting section to a periphery of the lens in which the width is along the direction perpendicular to the optical axis.
(1-33) In the objective lens of (1-21), a number m of a ring-shaped band through which a light ray of NA of 0.60 passes satisfies the following conditional formula:
22xe2x89xa6mxe2x89xa632
wherein a number of ring-shaped band located on an optical axis on a surface provided with the diffracting section is 1 and the number m is counted toward the periphery side.
(1-34) In the objective lens of (1-22), the diffracting section comprises a first diffracting section and a second diffracting section and an order number of a strongest diffracted light ray generated by the first diffracting section and an order number of a strongest diffracted light ray generated by the second diffracting section for a light flux having a predetermined wavelength are different from each other and not zero respectively.
(1-35) In the objective lens of (1-22), the diffracting section comprises a first diffracting section and a second diffracting section and an order number of a strongest diffracted light ray generated by the first diffracting section and an order number of a strongest diffracted light ray generated by the second diffracting section for a light flux having a predetermined wavelength are same to each other and not zero respectively.
(1-36) An optical information reproducing and/or recording apparatus to conduct reproducing and/or recording information of a first optical information recording medium. including a first transparent base plate having a thickness of t1 and a second optical information recording medium including a second transparent base plate having a thickness of t2 (t2 greater than t1), comprises:
an optical pickup apparatus comprising:
a first light source to emit a first light flux having a wavelength of xcex1;
a second light source to emit a second light flux having a wavelength of xcex2 (xcex1 less than xcex2);
a converging optical system to converge the first light or the second light flux onto a first information recording surface of the first optical information recording medium or a second information recording surface of the second optical information recording medium, the converging optical system having an objective lens; and
an optical detector to receive reflected light from the first optical information recording medium or the second optical information recording medium;
wherein the converging optical system comprises a diffracting section on an entire surface in an effective aperture or an almost entire surface in the effective aperture of at least one surface thereof,
the converging optical system generates a m-th order diffracted light ray (m being an integer other than zero) more than other order diffracted light rays when the first light flux passes the diffracting section and converges the m-th diffracted light ray onto the first information recording surface so as to conduct the reproducing and/or recording information of the first optical information recording medium;
the converging optical system generates a n-th order diffracted light ray (n being an integer other than zero) more than other order diffracted light rays when the second light flux passes the diffracting section and converges the n-th diffracted light ray onto the second information recording surface so as to conduct the reproducing and/or recording information of the second optical information recording medium; and
a spherical aberration has at least one discontinuous portion or at least one substantially discontinuous portion when the converging optical system converges the second light flux onto the second information recording surface so as to conduct reproducing and/or recording the information of the second optical information recording medium.
Further, above objects can be also attained by the following preferable structures.
(2-1) In an optical element usable in an optical pickup apparatus, at least one surface being a diffracting surface, wherein when an optical path difference function of the diffracting surface is xcfx86(h) where h is a distance from the optical axis, the optical path difference function is a discontinuous function in which dxcfx86(h)/dh is discontinuous or substantially discontinuous at a point where h is a predetermined distance.
(2-2) In the optical element described in (2-1), the width in the perpendicular direction to the optical axis in the most outside ring-shaped band in the ring-shaped bands formed inside the predetermined length h of the optical element is not larger than the width in the perpendicular direction to the optical axis in the ring-shaped band which adjoins the most outside ring-shaped band and is formed outside the predetermined length h.
(2-3) In the optical element described in (2-1) or (2-2), when the light is irradiated from the light source with the wavelength xcex2 located at a predetermined object distance onto the optical information recording medium having the transparent thickness t2 through the optical element, in the numerical aperture NA not larger than the predetermined distance h, the wave-front aberration is not larger than 0.07 xcex2 rms, and the spherical aberration of the light rays passing through the inside of the predetermined distance h is not larger than the spherical aberration of the light rays passing through the outside of the predetermined distance h by 10 xcex2xe2x88x92100 xcex2.
(2-4) In the optical element described in one of (2-1) to (2-3), at least one surface of the optical element is the diffraction surface having the diffracting ring-shaped band, and the i-th diffracting ring-shaped band of the at least one diffraction surface, counted from the optical axis toward the peripheral direction, satisfies the following conditional expression:
1.2xe2x89xa6Pi+1/Pixe2x89xa610xe2x80x83xe2x80x83(2)
where, Pi: the width in the direction perpendicular to the optical axis of the i-th diffracting ring-shaped band counted from the optical axis toward the peripheral direction.
(2-5) In an optical element usable in an optical pickup apparatus, at least one surface of the optical element is the diffraction surface having the diffracting ring-shaped band, and the i-th diffracting ring-shaped band of the at least one -diffraction surface, counted from the optical axis toward the peripheral direction, satisfies the following conditional expression:
1.2xe2x89xa6Pi+1/Pixe2x89xa610xe2x80x83xe2x80x83(2)
where, Pi: the width in the direction perpendicular to the optical axis of the i-th diffracting ring-shaped band counted from the optical axis toward the peripheral direction.
(2-6) In the optical element applicable for the optical pick-up apparatus, the number m of the diffracting ring-shaped band of the diffraction surface through which the light rays of NA 0.60 pass, satisfies
22xe2x89xa6mxe2x89xa632,
where, the number of the diffracting ring-shaped band of the ring-shaped band on the optical axis is 1, and the number of the diffracting ring-shaped band is counted toward the outside.
(2-7) In the optical element applicable for the optical pick-up apparatus, at least one surface is a diffraction surface having the diffracting ring-shaped band, and the number m of the diffracting ring-shaped band of the diffraction surface through which the light rays of NA 0.60 pass, satisfies
xe2x80x8322xe2x89xa6mxe2x89xa632,
where, the number of the diffracting ring-shaped band of the ring-shaped band on the optical axis is 1, and the number of the diffracting ring-shaped band is counted toward the outside.
(2-8) In the optical element described in (2-6) or (2-7), light rays of the optical element are almost parallel light flux within the range of the wavelength 630-665 nm, and entered into the optical element.
(2-9) In the optical element described in (2-1) or (2-8), the optical element is the objective lens.
(2-10) In an objective lens applicable for the optical pick-up apparatus having the converging optical system including the objective lens for converging the light flux from the light sources having the different wavelengths, and the light receiving means for detecting the reflected light from the recording surface, which can record or reproduce the information for at least two of the first and the second optical information recording medium whose transparent thickness is different from each other, when two wavelengths different from each other are xcex1 and xcex2 (xcex1 less than xcex2), and the thickness of the transparent substrates of two optical information recording media different from each other are t1 and t2 (t1 less than t2), and when the necessary numerical aperture on the image side necessary for recording or reproducing the optical information recording medium with the thickness t1 of the transparent substrate by the light flux of the wavelength xcex1 is NA1, and the necessary numerical aperture on the image side necessary for recording or reproducing the optical information recording medium with the thickness t2 of the transparent substrate by the light flux of the wavelength xcex2 is NA2 (NA1xe2x89xa7NA2), the wave front aberration is not larger than 0.07 xcex1 rms for the combination of the wavelength xcex1, thickness t1 of the transparent substrate, and necessary numerical aperture NA1, and the wave front aberration is not larger than 0.07 xcex2 rms for the combination of the wavelength xcex2, thickness t2 of the transparent substrate, and necessary numerical aperture NA2, and the light flux not smaller than the necessary numerical aperture NA2 is made a flare, for the combination of the wavelength xcex2, and thickness t2 of the transparent substrate.
(2-11) In the objective lens described in (2-10), when the light is irradiated from the light source with the wavelength xcex2 at a predetermined object distance onto the optical information recording medium with the transparent substrate thickness t2 through the objective lens, the light flux of the numerical aperture not smaller than NA2 and not larger than NA1, is distributed in the range of not smaller than the diameter w2 and not larger than the diameter w1, and satisfies the following conditional expressions:
10 xcexcmxe2x89xa6w2xe2x89xa650 xcexcmxe2x80x83xe2x80x83(3)
20 xcexcmxe2x89xa6w1xe2x88x92w2xe2x89xa6110 xcexcmxe2x80x83xe2x80x83(4)
(2-12) In the objective lens described in (2-10) or (2-11), at least one surface of the objective lens is the diffraction surface having the diffracting ring-shaped band, and when the optical path difference function of the diffraction surface is (h is the distance from the optical axis), xcfx86(h)/dh at a portion of the predetermined distance h is a discontinuous or practically discontinuous function.
(2-13) In the objective lens described in (2-12), the width in the perpendicular direction to the optical axis in the most outside ring-shaped band in the ring-shaped bands formed inside the predetermined distance h of the objective lens is not larger than the width in the perpendicular direction to the optical axis in the ring-shaped band which adjoins the most outside ring-shaped band and is formed outside the predetermined distance h.
(2-14) In the objective lens described in (2-12) or (2-13), when the light is irradiated from the light source of the wavelength xcex2 located at a predetermined object distance onto the optical information recording medium with the transparent substrate thickness t2 through the objective lens, in the numerical aperture NA not larger than the predetermined distance h, the spherical aberration is not larger than 0.07 xcex2 rms, and the spherical aberration of the light rays passing though the inside of the predetermined distance h is not larger than the spherical aberration of the light rays passing through the outside of the predetermined distance h by 10 xcex2-100 xcex2.
(2-15) In the objective lens described in one of (2-10) or (2-14), at least one surface of the objective lens is the diffraction surface having the diffracting ring-shaped band, and the i-th diffracting ring-shaped band counted from the optical axis toward the peripheral direction, of the at least one diffraction surface, satisfies the following conditional expression:
1.2xe2x89xa6Pi+1/Pixe2x89xa610,
where, P: the width in the perpendicular direction to the optical axis of the i-th diffracting ring-shaped band, counted from the optical axis toward the peripheral direction.
(2-16) In the objective lens described in one of (2-10) or (2-15), the number m of the diffracting ring-shaped band of the diffraction surface through which the light ray of NA 0.60 of the objective lens passes, satisfies 22xe2x89xa6mxe2x89xa632.
(2-17) In the objective lens described in one of (2-10) or (2-16), because the wavelength xcex1 is within the range of 630-665 nm, preferably 635 nm or 650 nm, the wavelength xcex2 is within 750-810 nm, preferably 780 nm, the thickness t1 is 0.6 mm, and the thickness t2 is 1.2 mm, the objective lens is appropriate for the optical pick-up apparatus which can record and/or reproduce the information for both of the DVD and CD.
(2-18) In the objective lens described in one of (2-10) or (2-17), because the first optical information recording medium is DVD and the second optical information recording medium is CD, the objective lens appropriate for the optical pick-up apparatus which can record and/or reproduce the information for both of the DVD and CD, can be provided.
(2-19) In an optical pick-up apparatus having the converging optical system including the objective lens for converging the light flux from the light sources having the different wavelengths, and the light receiving means for detecting the reflected light from the recording surface, which can record or reproduce the information for at least two of the first and the second optical information recording media whose transparent thickness is different from each other, when two wavelengths different from each other are xcex1 and xcex2 (xcex1 less than xcex2), and the thickness of the transparent substrates of two optical information recording media different from each other are t1 and t2 (t1 less than t2), and when the necessary numerical aperture on the image side necessary for recording or reproducing the optical information recording medium with the thickness t1 of the transparent substrate by the light flux of the wavelength xcex1 is NA1, and the necessary numerical aperture on the image side necessary for recording or reproducing the optical information recording medium with the thickness t2 of the transparent substrate by the light flux of the wavelength xcex2 is NA2 (NA1xe2x89xa7NA2), the wave. front aberration is not larger than 0.07 xcex1 rms for the combination of the wavelength xcex1, thickness t1 of the transparent substrate, and necessary numerical aperture NA1, and the wave front aberration is not larger than 0.07 xcex2 rms for the combination of the wavelength xcex2, thickness t2 of the transparent substrate, and necessary numerical aperture NA2, and the light flux not smaller than the necessary numerical aperture NA2 is made a flare, for the combination of the wavelength xcex2 and the thickness t2 of the transparent substrate.
(2-20) In the optical pickup apparatus described in (2-19), when the light is irradiated from the light source with the wavelength xcex2 located at a predetermined object distance onto the optical information recording medium with the transparent substrate thickness t2 through the objective lens, the light flux of not smaller than numerical aperture NA2 and not larger than NA1 distributes in the range of not smaller than the diameter w2 and not larger than w1, and satisfies the following conditional expressions:
10 xcexcmxe2x89xa6w2xe2x89xa650 xcexcm
20 xcexcmxe2x89xa6w1xe2x88x92w2xe2x89xa6110 xcexcm
(2-21) In the optical pickup apparatus described in (2-19) or (2-20), at least one surface of the objective lens of the optical pick-up apparatus is the diffraction surface having the diffracting ring-shaped band, and when the optical path difference function of the diffraction surface is xcfx86(h)(h is the distance from the optical axis), xcfx86(h)/dh is the discontinuous or practically discontinuous function at a portion of a predetermined distance h.
(2-22) In the optical pickup apparatus described in (2-21), in the diffracting ring-shaped band of at least one surface of the objective lens of the optical pick-up apparatus, the width in the perpendicular direction to the optical axis in the most outside ring-shaped band in the ring-shaped bands formed inside the predetermined distance h is not larger than the width in the perpendicular direction to the optical axis in the ring-shaped band which adjoins the most outside ring-shaped band and is formed outside the predetermined distance h.
(2-23) In the optical pickup apparatus described in (2-21) or (2-22), when the light is irradiated from the light source of the wavelength xcex2 located at a predetermined object distance onto the optical information recording medium with the transparent substrate thickness t2 through the objective lens of the optical pick-up apparatus, in the numerical aperture NA not larger than the predetermined distance h, the spherical aberration is not larger than 0.07 xcex2 rms, and the spherical aberration of the light rays passing though the inside of the predetermined distance h is not larger than the spherical aberration of the light rays passing through the outside of the predetermined distance h by 10 xcex2-1002.
(2-24) In the optical pickup apparatus described in one of (2-19) to (2-23), at least one surface of the objective lens is the diffraction surface having the diffracting ring-shaped band, and the i-th diffracting ring-shaped band counted from the optical axis toward the peripheral direction, of the at least one diffraction surface, satisfies the following conditional expression:
1.2xe2x89xa6Pi+1/Pixe2x89xa610
where, P: the width in the perpendicular direction to the optical axis of the i-th diffracting ring-shaped band, counted from the optical axis toward the peripheral direction.
(2-25) In the optical pickup apparatus described in one of (2-19) to (2-24), the number m of the diffracting ring-shaped band of the diffraction surface through which the light ray of NA 0.60 passes, satisfies 22xe2x89xa6mxe2x89xa63.
(2-26) In the optical pickup apparatus described in one of (2-19) to (2-25), the object point of the objective lens for the combination of the wavelength xcex1 and the thickness t1 of the transparent substrate, is at an optically equal distance to the object point of the objective lens for the combination of the wavelength xcex2 and the thickness t2 of the transparent substrate.
(2-27) In the optical pickup apparatus described in one of (2-19) to (2-26), the wavelength xcex1 is within the range of 630-665 nm, preferably 635 nm or 650 nm, the wavelength xcex2 is within 750-810 nm, preferably 780 nm, the thickness t1 is 0.6 mm, and the thickness t2 is 1.2 mm.
(2-28) In the optical pickup apparatus described in one of (2-19) to (2-28), the first optical information recording medium is DVD and the second optical information recording medium is CD.
(2-29) In an objective lens applicable for the optical pick-up apparatus, at lest one surface is the diffraction surface having the diffracting ring-shaped band, and the spherical aberration when the light flux of the wavelength xcex2 in the range of the numerical aperture NA of 0.5-0.7 passes through the objective lens is not smaller than the spherical aberration when the light flux of the wavelength xcex2 in the numerical aperture NA not larger than 0.5 passes through the objective lens by 10 xcex2-100 xcex2.
(2-30) In an optical pick-up apparatus having a light source to record and/or reproduce the information on the information recording surface of the optical information recording medium by irradiating the light with different wavelengths corresponding to 2 optical information recording media whose thickness of transparent substrates is different from each other, and an objective lens through which the light from the light source respectively passes, and which outputs the light to the optical information recording medium, at lest one surface of the objective lens is the diffraction surface having the diffracting ring-shaped band, and the spherical aberration when the light flux of a predetermined wavelength xcex2 in the range of the numerical. aperture NA of 0.5-0.7 passes through the objective lens is not smaller than the spherical aberration when the light flux of the predetermined wavelength xcex2 in the numerical aperture NA not larger than 0.5 passes through the objective lens by more than 10 xcex2-100 xcex2.
(2-31) In an objective lens applicable for the optical pick-up apparatus which has the light source with the wavelength xcex, the converging optical system including the objective lens for converging the light flux from the light source onto the recording surface of the optical information recording medium, and the light receiving means having the light receiving surface for detecting the reflected light from the recording surface, and can record or reproduce the information for the optical information recording medium, the objective lens has the diffraction surface on at least one surface, and when the light flux of the wavelength xcex of the numerical aperture NA of not larger than 0.5 passes, the light flux reflected from the optical information recording medium is irradiated to the light receiving means so that the light flux is included in the light receiving surface of the light receiving means, and when the light flux of the wavelength xcex of the numerical aperture NA of not smaller than 0.5 passes, the light flux reflected from the optical information recording medium is irradiated onto the surrounding except the light receiving surface of the light receiving means.
(2-32) In the objective lens applicable for the optical pick-up apparatus described in (2-31), the light receiving means has one to three almost rectangular light receiving surfaces and the spot diameter on the optical information recording surface of the light flux not smaller than the numerical aperture NA of 0.5 is not smaller than 5 xcexcm.
(2-33) In the objective lens applicable for the optical pick-up apparatus described in (2-31), the light receiving means has 3 rectangular light receiving surfaces aligned almost on a straight line and the spot diameter on the optical information recording surface of the light flux not smaller than the numerical aperture NA of 0.5 is not smaller than 25 xcexcm.
(2-34) In an objective lens applicable for the optical pick-up apparatus which has the light source with the wavelength xcex, the converging optical system including the objective lens for converging the light flux from the light source onto the recording surface of the optical information recording medium, and the light receiving means having the central light receiving surface and the peripheral light receiving surface for detecting the reflected light from the recording surface, and can record or reproduce the information for the optical information recording medium, the objective lens has the diffraction surface on at least one surface, and when the light flux of the wavelength xcex of the numerical aperture NA of not smaller than 0.5 passes, the light flux reflected from the optical information recording medium is irradiated to the light receiving means so that the light flux includes only the peripheral light receiving surface.
(2-35) In the objective lens applicable for the optical pick-up apparatus described in (2-34), the light receiving means has at least 2 stripe-like light receiving surfaces and the spot diameter on the optical information recording surface of the light flux not smaller than the numerical aperture NA of 0.5 is not smaller than 20 xcexcm.
(2-36) In the objective lens applicable for the optical pick-up apparatus described in (2-34), the light receiving means has at least 4 stripe-like light receiving surfaces, and the spot diameter on the optical information recording surface of the light flux not smaller than the numerical aperture NA of 0.5 is not smaller than 50 xcexcm.
(2-37) In an optical pick-up apparatus which has the light source with the wavelength xcex, the converging optical system including the objective lens for converging the light flux from the light source onto the recording surface of the optical information recording medium, and the light receiving means having the light receiving surface for detecting the reflected light from the recording surface, and can record or reproduce the information for the optical information recording medium, the objective lens has the diffraction surface on at least one surface, and when the light flux of the wavelength xcex of the numerical aperture NA of not larger than 0.5 passes, the light flux reflected from the optical information recording medium is irradiated to the light receiving means so that the light flux is included in the light receiving surface of the light receiving means, and when the light flux of the wavelength xcex of the numerical aperture NA of not smaller than 0.5 passes, the light flux reflected from the optical information recording medium is irradiated to the surrounding except the light receiving surface of the light receiving means.
(2-38) In the optical pick-up apparatus described in (2-37), the light receiving means has 1 to 3 almost rectangular light receiving surfaces and the spot diameter on the optical information recording surface of the light flux not smaller than the numerical aperture NA of 0.5 is not smaller than 5 xcexcm.
(2-39) In the optical pick-up apparatus described in (2-37), the light receiving means has 3 rectangular light receiving surfaces aligned almost on a straight line and the spot diameter on the optical information recording surface of the light flux not smaller than the numerical aperture NA of 0.5 is not smaller than 25 xcexcm.
(2-40) In an optical pick-up apparatus which has the light source with the wavelength xcex, the converging optical system including the objective lens for converging the light flux from the light source onto the recording surface of the optical information recording medium, and the light receiving means having the central light receiving surface and the peripheral light receiving surface for detecting the reflected light from the recording surface, and can record or reproduce the information for the optical information recording medium, the objective lens has the diffraction surface on at least one surface, and when the light flux of the wavelength xcex of the numerical aperture NA of not smaller than 0.5 passes, the light flux reflected from the optical information recording medium is irradiated to the light receiving means so that the light flux includes only the peripheral light receiving surface.
(2-41) In the optical pick-up apparatus described in (2-40), the light receiving means has at least 2 stripe-like light receiving surfaces and the spot diameter on the optical information recording surface of the light flux not smaller than the numerical aperture NA of 0.5 is not smaller than 20 xcexcm.
(2-42) In the optical pick-up apparatus described in (2-40), the light receiving means has at least 4 stripe-like light receiving surfaces and the spot diameter on the optical information recording surface of the light flux not smaller than the numerical aperture NA of 0.5 is not smaller than 50 xcexcm.
(3-1) An optical pick-up apparatus is structured such that the light flux from the light source is converged onto the information recording surface by the converging optical system including the objective lens through the transparent substrate of the optical information recording medium, and recording or reproducing of the information is conducted, and the optical pick-up apparatus conducts recording or reproducing of the information of at least 2 kinds of optical information recording media in which the thickness of the transparent substrate and recording density are different; and in the optical pick-up apparatus which has the first light source with the wavelength xcex1 (nm), the second light source with the wavelength xcex2 (nm) (xcex2 greater than xcex1), and a light detector which receives the reflected light from the optical information recording medium of the emitted light flux from the first light source and the second light source, and in which the necessary numerical aperture on the optical information recording medium side of the converging optical system necessary for recording or reproducing the first optical information recording medium whose transparent substrate thickness is t1 by the wavelength xcex1, is NA1, and the necessary numerical aperture on the optical information recording medium side of the converging optical system necessary for recording or reproducing the second optical information recording medium whose transparent substrate thickness is t2 (herein, t2 greater than t1) by the wavelength xcex2, is NA2 (herein, NA2 less than NA1), and when the diffraction pattern is provided on at least one surface of the converging optical system, and m-degree diffraction light (m is an integer) from the diffraction pattern of the converging optical system of the light flux from the first light source is at least used, the first optical information recording medium whose transparent substrate thickness is t1 is recorded and/or reproduced, and when n-degree diffraction light (n is an integer, and n=m=0 is excepted)) from the diffraction pattern of the converging optical system of the light flux from the second light source is at least used, the second optical information recording medium whose transparent substrate thickness is t2 (t2 greater than t1) is recorded and/or reproduced, in the light flux from the second light source passed through the objective lens, the tertiary spherical aberration component of the wave front aberration when the light flux of a portion in which the numerical aperture is lower than NA2, on the optical information recording medium side, passes through the transparent substrate of the second optical information recording medium, is excessive, and when the absolute value is WSA2 xcex2 rms, then,
0.02 xcex2 rmsxe2x89xa6WSA2xe2x89xa60.06 xcex2 rms.
(3-2) In the optical pickup apparatus described in (3-1), m is an integer excluding 0 and n=m.
(3-3) In the optical pickup apparatus described in (3-1) or (3-2), the objective lens is a single lens and the diffraction pattern is provided on the single lens.
(3-4) In the optical pickup apparatus described in (3-1), (3-2) or (3-3), when the. image formation magnification viewed from the optical information recording medium side of the objective lens at the time of recording or reproducing of the information of the first optical information recording medium is M1 and the image formation magnification viewed from the optical information recording medium side of the objective lens at the time of recording or reproducing of the information of the second optical information recording medium is M2, M2 and M1 is nearly equal.
(3-5) In the optical pickup apparatus described in (3-4), M1 and M2 are nearly 0.
(3-6) In the optical pickup apparatus described in one of (3-1) to (3-5), the position onto which the light ray most apart from the optical axis in the light flux from the second light source passed the objective lens, is converged through the transparent substrate of the second optical information recording medium, is far from the objective lens, and farther than the position at which, in the light flux from the second light source passed the objective lens, the wave front aberration is minimum, when the light flux of a portion in which the numerical aperture on the optical information recording medium side is smaller than NA2, passes through the transparent substrate of the second optical information recording medium, and its difference is not smaller than 5 xcexcm. When the difference is not smaller than 5 xcexcm.
(3-7) In the optical pickup apparatus described in one of (3-1) to (3-5), the position onto which the light ray most apart from the optical axis in the light flux from the second light source passed the objective lens, is converged through the transparent substrate of the second optical information recording medium, is, far from the objective lens, and farther than the position at which, in the light flux from the second light source passed through the objective lens, the wave front aberration is minimum, when the light flux of a portion in which the numerical aperture on the optical information recording medium side is smaller than NA2, passes through the transparent substrate of the second optical information recording medium, and its difference is not smaller than 15 xcexcm.
(3-8) An optical pick-up apparatus is structured such that the light flux from the light source is converged onto the information recording surface by the converging optical system including the objective lens through the transparent substrate of the optical information recording medium, and recording or reproducing of the information is conducted, and the optical pick-up apparatus conducts recording or reproducing the information of at least 2 kinds of optical information recording media in which the thickness of the transparent substrates and recording density are different and in the optical pick-up apparatus which has the first light source with the wavelength xcex1 (nm), the second light source with the wavelength xcex2 (nm) (xcex2 greater than xcex1), and a light detector which receives the reflected light from the optical information recording medium of the emitted light flux from the first light source and the second light source, and the necessary numerical aperture on the optical information recording medium side of the converging optical system necessary for recording or reproducing the first optical information recording medium whose transparent substrate thickness is t1, by the wavelength xcex1, is NA1, and the necessary numerical aperture on the optical information recording medium side of the converging optical system necessary for recording or reproducing the second optical information recording medium whose transparent substrate thickness is t2 (herein, t2 greater than t1) by the wavelength xcex2, is NA2 (herein, NA2 less than NA1), and when the almost ring-shaped band-like diffraction pattern is provided on at least one surface of the objective lens of the converging optical system, and m-degree diffraction light (m is an integer) from the diffraction pattern of the converging optical system of the light flux from the first light source is at least used, the first optical information recording medium whose transparent substrate thickness is t1 is recorded and/or reproduced, and when n-degree diffraction light (n is an integer, and n=m=0 is excepted)) from the diffraction pattern of the converging optical system of the light flux from the second light source is at least used, the second optical information recording medium whose transparent substrate thickness is t2 (t2 greater than t1) is recorded and/or reproduced, when the numerical aperture on the optical information recording medium side of the light ray passing the peripheral edge of the almost ting band-like diffraction pattern including the optical axis is NAX, then, 0.2xe2x89xa6NAX/NA2xe2x89xa60.9.
(3-9) In the optical pickup apparatus described in (3-8), m is an integer excluding 0 and n=m.
(3-10) In the optical pickup apparatus described in (3-8) or (3-9), the objective lens is a single lens.
(3-11) In the optical pickup apparatus described in (3-8), (3-8) or (3-10), when the image formation magnification viewed from the optical information recording medium side of the objective lens at the time of recording or reproducing of the information of the first optical information recording medium is M1 and the image formation magnification viewed from the optical information recording medium side of the objective lens at the time of recording or reproducing of the information of the second optical information recording medium is M2, M2 and M1 is nearly equal.
(3-12) In the optical pickup apparatus described in (3-11), M1 and M2 are nearly 0.
(3-13) In the optical pickup apparatus described in one of (3-8) to (3-12), the number of ring-shaped bands is 7 to 30.
(3-14) In the optical pickup apparatus described in (3-1), (3-2), (3-8) or (3-9), the light flux incident on the information recording surface is divided into at least 3 light flux of the first light flux in the vicinity of the optical axis, the second light flux outside the first light flux, and the third light flux outside the second light flux, and the second light flux is caused not to reach the vicinity of the information recording surface, by the shielding means, and in the m-degree diffraction light from the diffraction pattern of the converging optical system of the light flux from the first light source, the first light flux and the third light flux mainly form the beam spot, and records and/or reproduces the first optical information recording medium, and in the n-degree diffraction light from the diffraction pattern of the converging optical system of the light flux from the second light source, the first light flux mainly forms the beam spot, and records and/or reproduces the second optical information recording medium.
(3-15) In the optical pickup apparatus described in (3-14), the objective lens is single lens and the diffraction pattern is provided on the single lens.
(3-16) In the optical pickup apparatus described in (3-14) or (3-15), the objective lens is single lens and the shielding means is provided on the single lens.
(3-17) In the optical pickup apparatus described in (3-1), (3-2), (3-8) or (3-9), the light flux incident on the information recording surface is divided into at least 3 light flux of the first light flux in the vicinity of the optical axis, the second light flux outside the first light flux, and the third light flux outside the second light flux, and the beam spot is formed and the first optical information recording medium is recorded and/or reproduced, when the first light flux and the third light flux in the light flux from the first light source at least utilize the m-degree diffraction light from the diffraction pattern of the converging optical system, and the beam spot is formed and the second optical information recording medium is recorded and/or reproduced, when the first light flux and the third light flux at least utilize the n-degree diffraction light from the diffraction pattern of the converging optical system of the first light flux of the light flux from the second light source, and the second light flux.
(3-18) In the optical pickup apparatus described in (3-17), the convergent position of a most apart portion from the optical axis in the first light flux of the light flux from the second light source is different from the convergent position of the second light flux.
(3-19) In the optical pickup apparatus described in (3-17), the objective lens is a single lens and the diffraction pattern is provided on the single lens.
(3-20) In the optical pickup apparatus described in (3-17), (3-18) or (3-19), the second light flux is diffracted by the diffraction pattern.
(3-21) In the optical pickup apparatus described in (3-17), (3-18) or (3-19), the second light flux passes through a portion having no diffraction pattern.
(3-22) In the optical pickup apparatus described in (3-1), (3-2), (3-8) or (3-9), in the light flux from the second light source, the light flux in which the numerical aperture on the optical information recording medium side is more than NA3 (NA2xe2x89xa6NA3 less than NA1), is made not to reach in the vicinity of the information recording surface by the shielding means.
(3-23) In the optical pickup apparatus described in (3-22), the shielding means is preferably a ring-shaped band dichroic filter through which the light flux with the wavelength xcex1 passes and on which the light flux with the wavelength xcex2 is reflected.
(3-24) In the optical pickup apparatus described in one of (3-1) to (3-23), by the light flux of a portion in which the numerical aperture on the optical information recording medium side, in the n-degree diffraction light from the diffraction pattern of the converging optical system of the light flux from the second source is smaller than almost NA2, the beam spot is formed, and the second optical information recording medium is recorded and/or reproduced, and a portion in which the numerical aperture is larger than almost NA2 is the flare light.
(3-25) In the optical pickup apparatus described in one of (3-1) to (3-24), the first light source and the second light source are formed into a unit, and the light detector is common to the first light source and the second light source.
(3-26) An objective lens for use in an optical pick-up apparatus to conduct the recording or reproducing of the information for the optical information recording medium, has the diffraction pattern at least on one surface, and when the parallel light flux of the wavelength 780 nm are incident on the surface, the tertiary spherical aberration component of the wave front aberration when a portion in which the numerical aperture on the optical information recording medium side, is smaller than 0.45, in the light flux passed through the objective lens, passes through the transparent substrate of the thickness 1.2 mm, and the refractive index 1.57, is excessive, and the absolute value is WSA2 xcex2 rms, and in the case where the parallel light flux of the wavelength 650 nm are incident on the surface, when the absolute value of the tertiary spherical aberration component of the wave front aberration when a portion in which the numerical aperture on the optical information recording medium side is smaller than 0.6, in the light flux passed through the objective lens, passes through the transparent substrate of the thickness 0.6 mm and the referactive index 1.58, is WSA1 xcex1 rms, the following conditional expressions are satisfied:
0.02 xcex2 rmsxe2x89xa6WSA2xe2x89xa60.06 xcex2 rms, and
xe2x80x83WSA1xe2x89xa60.04 xcex1 rms.
(3-27) An objective lens for use in an optical pickup apparatus described has almost ring-shaped band-like diffraction pattern on the whole surface of the effective diameter of at least one surface, and when the height from the optical axis of the peripheral edge of the almost ring-shaped band-like diffraction pattern including the optical axis is HX, and the height of the most outer peripheral ring-shaped band is HMAX, the following conditional expression is satisfied:
0.15xe2x89xa6HX/HMAXxe2x89xa60.65
(3-28) In the objective lens for use in an optical pickup apparatus described in (3-27), the objective lens is a single lens.
(3-29) An objective lens for an optical pick-up has almost ring-shaped band-like diffraction pattern on the whole surface of the effective diameter of at least one surface and the spherical aberration is discontinuous at more than 2 portions at least for the light flux of some wavelength.
(3-30) An objective lens for an optical pick-up is a single lens and has almost ring-shaped band-like diffraction pattern on the whole surface of the effective diameter of one surface, and the other surface is a continuous surface, and the spherical aberration is discontinuous at 2 portions or more at least for the light flux of some wavelength.
(3-31) In an objective lens for an optical pick-up, a plurality of ring-shaped band-like diffraction patterns are provided on the optical axis portion and the periphery of the effective diameter on at least one surface, and the refractive surface is provided between the ring-shaped band and its adjoining ring-shaped band, and the spherical aberration is discontinuous on the boundary of the refractive surface and the diffraction pattern.
(3-32) In the objective lens for an optical pick-up described in (3-31), the objective lens is a single lens.
(3-33) In the objective lens for an optical pick-up described in (26-32), the number of ring-shaped bands of the diffraction is 7 to 30.
(4-1) In an objective lens for use in an optical pick-up apparatus for the information recording and reproducing which has the converging optical system including the objective lens to converge the light flux from the light sources having different wavelengths onto the recording surface of the optical disk, and a light receiving means for detecting the reflected light from the recording surface, and by which the information can be recorded or reproduced for the first and second optical disks whose transparent substrate thickness is different from each other, when the objective lens is formed of the fist lens having the positive refractive power and the second lens having the positive refractive power, in order from the laser light source, and at least one surface is the diffraction surface having the diffracting ring-shaped band, and 2 wavelengths different from each other are xcex1, xcex2 (xcex1 less than xcex2), the thickness of the transparent substrates, which are different from each other, of 2 information recording media are t1, t2 (t1 less than t2), the predetermined image side numerical aperture necessary for conducting the recording or reproducing onto the information recording medium with the thickness t1 of the transparent substrate by the light flux of the wavelength xcex1, is NA1, and the predetermined image side numerical aperture necessary for conducting the recording or reproducing onto the information recording medium with the thickness t2 of the transparent substrate by the light flux of the wavelength xcex2 is NA2 (NA1xe2x89xa7NA2), then, the wave front aberration is not larger than 0.07xcex1, rms, for the combination of the wavelength xcex1, the transparent substrate thickness t1 and the image side numerical aperture NA1, and the wave front aberration is not larger than 0.07 xcex2 rms, for the combination of the wavelength xcex2, the transparent substrate thickness t2 and the image side numerical aperture NA2.
(4-2) In the objective lens described in (4-1), the wave front aberration is not larger than 0.07 xcex2 rms for the combination of the wavelength xcex2, the transparent substrate thickness t2 and the image side numerical aperture NA2.
(4-3) In the objective lens described in (4-1) or (4-2), the wave front aberration is not smaller than 0.07xcex2 rms for the combination of the wavelength xcex2, the transparent substrate thickness t2 and the image side numerical aperture NA2.
(4-4) In the objective lens described in one of (4-1) to (4-3), for the combination of a predetermined position of the object point, the wavelength xcex1, and the transparent substrate thickness t1, the wave front aberration is not larger than 0.07 xcex1, rms, and for the combination of the object point at optically equal distance to the predetermined position, the wavelength xcex2 and the transparent substrate thickness t2, the wave front aberration is not larger than 0.07xcex2 rms.
(4-5) In the objective lens described in one of (4-1) to (4-3), for the combination of a predetermined position of the object point, the wavelength xcex1 and the transparent substrate thickness t1, the wave front aberration is not larger than 0.07xcex1, rms, and for the combination of the object point at optically not equal distance to the predetermined position, the wavelength 2 and the transparent substrate thickness t2, the wave front aberration is not larger than 0.07 xcex2 rms (xcex is respective wavelength).
(4-6) The objective lens described in one of (4-1) to (4-5) satisfies the following conditional expression:
0.4xe2x89xa6|(Ph/Pf)xe2x88x922|xe2x89xa625xe2x80x83xe2x80x83(5)
Where, Pf: the pitch of the diffracting ring-shaped band in the image side numerical aperture NA1 necessary for conducting the recording or reproducing onto the information recording medium with the transparent substrate thickness t1, and
Ph: the pitch of the diffracting ring-shaped band in the numerical aperture of xc2xd of NA1.
(4-7) The objective lens described in (4-6) satisfies the following conditional expression:
0.8xe2x89xa6(Ph/Pf)xe2x89xa62|xe2x89xa66.0
(4-8) The objective lens described in (4-6) satisfies the following conditional expression:
0.8xe2x89xa6|(Ph/Pf)xe2x88x922|xe2x89xa66.0
(4-9) The objective lens described in one of (4-1) to (4-8) satisfies the following conditional expression:
0.70xe2x89xa6d1/fxe2x89xa61.70
0.60xe2x89xa6r1/(n1xc2x7f)xe2x89xa61.10
0.3xe2x89xa6(r2+r1)(r2xe2x88x92r1)xe2x89xa62.0
Where, d1: the lens thickness on the axis of the first lens,
f: focal distance, ri: the paraxial radius of curvature of each surface, n1: the refractive index of the first lens.
(4-10) The objective lens described in (4-9) satisfies the following conditional expression:
1.00xe2x89xa6d1/fxe2x89xa61.40
0.70xe2x89xa6r/(n1xc2x7f)xe2x89xa60.90
0.4xe2x89xa6(r2+r1)/(r2xe2x88x92r1)xe2x89xa61.4
(4-11) In an optical pick-up apparatus for information recording and reproducing which has the converging optical system including the objective lens to converge the light flux from the light sources having different wavelengths onto the recording surface of the optical disk, and the light receiving means for detecting the reflected light from the recording surface, and by which the information can be recorded or reproduced for the first and second optical disks whose transparent substrate thickness is different from each other, (herein, the necessary numerical aperture for the objective lens of the first optical disk is larger than that of the second optical disk), when the objective lens is formed of the fist lens having the positive refractive power and the second lens having the positive refractive power, in order from the laser light source side, and at least one surface is the diffraction surface having the diffracting ring-shaped band, and when 2 wavelengths different from each other are xcex1, xcex2 (xcex1 less than xcex2), the thickness of the transparent substrates, which are different from each other, of 2 information recording media are t1, t2 (t1 less than t2), the redetermined image side numerical aperture necessary for conducting the recording or reproducing onto the information recording medium with the thickness t1 of the transparent substrate by the light flux of the wavelength xcex1 is NA1, and the predetermined image side numerical aperture necessary for conducting the recording or reproducing onto the information recording medium with the thickness t2 of the transparent substrate by the light flux of the wavelength xcex2 is NA2 (NA1xe2x89xa6NA2), then, the wave front aberration is not larger than 0.07xcex1 rms, for the combination of the wavelength xcex1, the transparent substrate thickness t1 and the image side numerical aperture NA1, and the wave front aberration is not larger than 0.07xcex2 rms, for the combination of the wavelength xcex2, the transparent substrate thickness t2 and the image side numerical aperture NA2.
(4-12) In the optical pickup apparatus described in (4-11), the wave front aberration of the objective lens is not larger than 0.07xcex2 rms for the combination of the wavelength xcex2, the transparent substrate thickness t2 and the image side numerical aperture NA1.
(4-13) In the optical pickup apparatus described in (4-11) or (4-12), the wave front aberration of the objective lens is not smaller than 0.07xcex2 rms for the combination of the wavelength xcex2, the transparent substrate thickness t2 and the image side numerical aperture NA1.
(4-14) In the optical pickup apparatus described in one of (4-11) to (4-13), for the combination of a predetermined position of the object point, the wavelength xcex1 and the transparent substrate thickness t1, the wave front aberration of the objective lens is not larger than 0.07xcex1 rms, and for the combination of the object point at optically equal distance to the predetermined position, the wavelength xcex2 and the transparent substrate thickness t2, the wave front aberration is not larger than 0.07xcex2 rms.
(4-15) In the optical pickup apparatus described in one of (4-11) to (4-14), for the combination of a predetermined position. of the object point, the wavelength xcex1 and the transparent substrate thickness t1, the wave front aberration of the objective lens is not larger than 0.07xcex1, rms, and for the combination of the object point at optically not equal distance to the predetermined position, the wavelength xcex2 and the transparent substrate thickness t2, the wave front aberration is not larger than 0.07xcex2 rms (xcex is respective wavelength).
(4-16) In the optical pickup apparatus described in one of (4-11) to (4-15), the objective lens satisfies the following conditional expression:
0.4xe2x89xa6|(Ph/Pf)xe2x88x922|xe2x89xa625
Where, Pf: the pitch of the diffracting ring-shaped band in the image side numerical aperture NA1 necessary for conducting the recording or reproducing onto the information recording medium with the transparent substrate thickness t1, and
Ph: the pitch of the diffracting ring-shaped band in the numerical aperture of xc2xd of NA1.
(4-17) In the optical pickup apparatus described in (4-16), the objective lens satisfies the following conditional expression:
0.8xe2x89xa6|(Ph/Pf)xe2x88x922|xe2x89xa66.0
(4-18) In the optical pickup apparatus described in (4-16), the objective lens satisfies the following conditional expression:
1.2xe2x89xa6|(Ph/Pf)xe2x88x922|xe2x89xa62.0
(4-19) In the optical pickup apparatus described in one of (4-11) to (4-18), the objective lens satisfies the following conditional expression:
0.70xe2x89xa6d1/fxe2x89xa61.70
0.60xe2x89xa6r1/(n1xc2x7f)xe2x89xa61.10
0.3xe2x89xa6(r2+r1)(r2xe2x88x92r1)xe2x89xa62.0
Where, d1: the lens thickness on the axis of the first lens,
f: focal distance, ri: the paraxial radius of curvature of each surface, n1: the refractive index of the first lens.
(4-20) In the optical pickup apparatus described in (4-19), the objective lens satisfies the following conditional expression:
1.00xe2x89xa6d1/fxe2x89xa61.40
0.70xe2x89xa6r1/(n1xc2x7f)xe2x89xa60.90
xe2x80x830.4xe2x89xa6(r2+r1)/(r2xe2x88x92r1)xe2x89xa61.4
(5-1) An optical-element for use in an optical pick-up apparatus for reproducing the information from the optical information recording medium or recording the information onto the optical information recording medium, has the optical axis and the diffraction portion, and the diffraction portion has a plurality of areas, and the number of degrees of the diffracted light at which the plurality of areas most intensively generate for respective predetermined wavelengths, is not respectively 0, and the absolute value is different from each other.
(5-2) In the optical element described in (5-1), the diffraction portion of the optical element has the diffracting ring-shaped band in each of the plurality of areas, and most intensively generates the diffraction light of the first degree (n1xe2x89xa00) in the inside of a predetermined distance from the optical axis, and in its outside, most intensively generates the second degree diffraction light (n2xe2x89xa00, and |n1|xe2x89xa0|n2|), which is different from the fist degree.
(5-3) In the optical element described in (5-1), the diffraction portion of the optical element has the diffracting ring-shaped band for each of the plurality of areas, and the maximum value of the difference in level in the diffracting ring-shaped band and the minimum value of the difference in level are different by more than 1.5 times, thereby, in the inside of the predetermined distance from the optical axis, the diffraction light of the first degree (n1xe2x89xa00) is generated most intensively, and in its outside, the diffraction light of the second degree, different from the fist degree (n2xe2x89xa00, and |n1|xe2x89xa0n2|), is generated most intensively.
(5-4) In the optical element described in (5-3), the maximum vale of the difference in level and the minimum value of the difference in level of the optical element are not different from each other more than 6 times.
(5-5) In the optical element described in one of (5-2) to (5-4), when the first degree of the optical element is n1, and the second degree is n2, n1=1 and n2xe2x89xa72 are realized (herein, the sign of the diffraction degree is determined such that a sign when the light flux is changed in the converging direction by the diffraction is positive).
(5-6) In the optical element described in (5-5), n2=2 is realized.
(5-7) In the optical element described in one of (5-2) to (5-6), the diffracting ring-shaped band of the optical element is blazed so that the diffraction efficiency becomes maximum for the first degree diffraction light of a predetermined wavelength in the inside of the predetermined distance from the optical axis, and it is blazed so that the diffraction efficiency becomes maximum for the second degree diffraction light of a wavelength different from the predetermined wavelength in the outside of a predetermined distance from the optical axis.
(5-8) In the optical element described in one of (5-2) to (5-7), the optical element is an objective lens for use in the optical pick-up apparatus.
(5-9) An optical pickup apparatus reproduces the information from the optical information recording medium, or records the information onto the optical information recording medium, by using the optical element described in one of (5-2) to (5-8).
(5-10) An optical pick-up apparatus which reproduces the information from at least 2 kinds of optical information recording media, or records the information onto the optical information recording media, has: the first light source to emit the first light flux having the first wavelength xcex1; the second light source to emit the second light flux having the second wavelength xcex2 which is different from the first wavelength xcex1; the converging optical system including the objective lens to converge the fist light flux and the second light flux emitted from the first light source and the second light source onto the information recording surfaces through the transparent substrates of the first and the second optical information recording media; and the light detector receiving the reflected light from the first and the second optical information recording media, wherein the objective lens has the optical axis and diffraction portion, the diffraction portion has a plurality of areas, and the degrees in which the plurality of areas most intensively generate respectively for the predetermined wavelength, are respectively not 0, and the absolute values are different from each other, the first light source emits the first light flux for reproducing the information from the first optical information recording medium having the first transparent substrate with the thickness t1, or for recording the information, the second light source emits the second light flux for reproducing the information from the second optical information recording medium having the second transparent substrate with the thickness t2 different from the thickness t1, or for recording the information, the converging optical system can converge the light flux from the first light source onto the information recording surface of the first optical information recording medium, under the condition in which the wave front aberration is not larger than 0.07 xcex1 rms in the predetermined numerical aperture NA1 on the image side of the objective lens necessary for recording or reproducing of the first optical information recording medium, by the light flux of the wavelength xcex1, and can converge the light flux from the second light source onto the information recording surface of the second optical information recording medium, under the condition in which the wave front aberration is not larger than 0.07 xcex2 rms in the predetermined numerical aperture NA2 on the image side of the objective lens necessary for recording or reproducing of the second optical information recording medium, by the light flux of the wavelength xcex2, and further, satisfies the following conditions:
xcex1 less than xcex2
t1 less than t2
NA1 greater than NA2
(5-11) In the optical pickup apparatus described in (5-10), the diffraction portion of the optical element has the diffracting ring-shaped band in each of the plurality of areas, and most intensively generates the diffraction light of the first degree (n1xe2x89xa00) in the inside of a predetermined distance from the optical axis, and in its outside, most intensively generates the second degree diffraction light (n2xe2x89xa00, and |n1|xe2x89xa0n2|), which is different from the first degree.
(5-12) In the optical pickup apparatus described in (5-10), the diffraction portion of the optical element has the diffracting ring-shaped band for each of the plurality of areas, and the maximum value of the difference in level in the diffracting ring-shaped band and the minimum value of the difference in level are different by more than 1.5 times, thereby, in the inside of the predetermined distance from the optical axis, the diffraction light of the first degree (n1xe2x89xa00) is generated most intensively, and in its outside, the diffraction light of the second degree, different from the fist degree (n2xe2x89xa00, and |n1|xe2x89xa0n2|), is generated most intensively.
(5-13) In the optical pickup apparatus described in (5-11) or (5-12), in the outside of the predetermined distance from the optical axis of the pick-up apparatus, the minimum pitch of the diffracting ring-shaped band in the effective diameter, is not smaller than 10 xcexcm and not larger than 80 xcexcm.
(5-14) In the optical pickup apparatus described in (5-13), the maximum vale of the difference in level and the minimum value of the difference in level of the optical pick-up apparatus are not different from each other more than 6 times.
(5-15) In the optical pickup apparatus described in one of (5-11) to (5-14), when the first degree of the optical pick-up apparatus is n1, and the second degree is n2, n1=1 and n2xe2x89xa72 are realized (herein, the sign of the diffraction degree is determined such that a sign when the light flux is changed in the converging direction by the diffraction is positive).
(5-16) In the optical pickup apparatus described in (5-15), n2=2 is realized.
(5-17) In the optical pickup apparatus described in one of (5-11) to (5-16), the diffracting ring-shaped band of the optical pick-up apparatus is blazed so that the diffraction efficiency becomes maximum for the first degree diffraction light of a predetermined wavelength in the inside of the predetermined distance from the optical axis, and it is blazed so that the diffraction efficiency becomes maximum for the second degree diffraction light of a wavelength different from the predetermined wavelength in the outside of a predetermined distance from the optical axis.
(5-18) In the optical pickup apparatus described in one of (5-10) to (5-17), the converging optical system converges the light flux from the second light source onto the information recording surface of the second optical information recording medium under the condition that the wave front aberration is not smaller than 0.07 xcex2 rms in the numerical aperture NA1.
(5-19) In the optical pickup apparatus described in one of (5-10) to (5-18), the predetermined distance of the diffraction portion in the objective lens is almost corresponding to a range through which the light flux of NA2 passes.
(5-20) In the optical pickup apparatus described in one of (5-10) to (5-19), in the converging optical system, the spherical aberration is discontinuous at a predetermined distance from the optical axis for the light flux with the wavelength xcex2.